Method of copying



April W, 1966 T. G. WARTMAN ETAL 3,24fi,@

METHOD OF COPY ING Original Filed May 12, 1961 United States Patent 3,246,600 METHOD OF COPYING Thomas G. Wartman, Mendota Heights, and Gerhard W. R. Pnerclrhauer, Maplewood, Minn, assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware Original application May 12, 1961, Ser. No. 109,761, now Patent No. 3,149,563, dated Sept. 22, 1964. Divided and this application Oct. 28, 1963, Ser. No. 319,365

2 Claims. (Cl. 101-129) This invention relates to the preparation by thermographic copying methods of novel stencil-like intermediates from which multiple copies may be produced, in particular by simple heating of the intermediate in con tact with a suitable receptor sheet.

This application is a division of our application Serial No. 109,761, filed May 12, 1961, now Patent No. 3,149,563.

In a typical example, a radiation-transmissive intermediate heat-sensitive sheet material as hereinafter described is placed in heat-conductive contact with a differentially radiation-absorptive graphic original which is then briefly exposed, through the sheet material, to intense radiation to provide a heat-pattern which produces in the contacting sheet material a corresponding stencil pattern. The sheet material. is then placed in contact with a suitable receptor sheet and is briefly heated, for example in an ironing-machine. A duplicate copy of the original is produced on the receptor sheet. Additional copies are produced on repeating this step of the process with additional receptor sheets.

In the drawing,

FIGURE 1 illustrates the irradiation of a graphic original through an intermediate sheet material 11, comprising inner film 12, central layer 13, and outer film 14-, with radiation 15 to provide a stencil-like pattern 16 in film 12 corresponding to the radiation-absorptive image area 17;

FIGURE 2 illustrates the transfer of image-forming material from the central layer 13 through the pattern 16 in the film 12 under the influence of heat appiled as indicated by wavy arrows 20, to form on the receptor sheet 18 a visible duplicate 19 of the original image area 17; and

FIGURE 3 illustrates another method of copying in which an intermediate sheet 40, in this case consisting of fibrous support layer 42 and thin film layer 41, previously subjected to a heat-pattern as in FIGURE 1 to provide pattern areas 46, is placed in contact with a visibly heat-sensitive copy-sheet 48 which is partially radiationabsorptive, and. the composite is briefly subjected to intense radiation 45, producing visible image areas 47 in the heat-sensitive copysheet.

The stencil-forming intermediate sheet material will be seen to provide a number of advantages. The form illustrated in FIGURES l .and 2 may contain any of a wide variety of image-forming components within the central layer 13, the same being fully covered and protected by the surface film layers 12 and 14. Contact of the imageforming components with other surfaces, for example with paper originals or receptors or with the hands of an operator, is avoided. Loss of liquid or volatile materials is prevented. The sheet serves as a reservoir of imageforming material so that large numbers of copies may be made.

The copying procedure illustrated in FIGURES 1 and 2 involves the formation of a heat-pattern at the radiation-absorptive image area 17, resulting in the formation of numerous tiny channels or apertures through the areas of the thin film 12 associated therewith. Image-forming materials contained in the central layer 13 and between the films 12 and 14 are then transferred from the intermediate through the perforate image areas 16 to suitable receptor sheets for formation of the desired image. As the image-forming material is depleted from the space immediately above' the channeled area 16, more is continuously supplied from adjacent areas of the central layer 13.

The image-forming material may for example be in the form of colored fusible solids such as waxes containing dyes or pigments, colored liquids such as viscous inks, volatile coloring agents such as volatile organic dyes, and colored or colorless transferable reactant materials capable of undergoing a color-forming reaction with coreactant materials present in the receptor sheet. Colorless or slightly colored materials which may subsequently be converted to strongly colored form or, being ink-receptive, may subsequently be selectively coated with liquid or powdered inks or other coloring agents, may likewise be employed as image-forming components in the central layer 13 of the intermediate sheet materials.

The image-forming components are retained within the fibrous central layer of the sheet material both for convenience in assembling the several layers and, particularly in. the case of normally liquid or low-melting solid materials, as a means'of maintaining such materials in position within the assembly. Thin porous paper is conveniently used for this purpose, but other thin absorbent webs are equally satisfactory. They may be fastened to the surface films by means of direct fusion or embedding, or by means of adhesive coatings which may additionally serve to reinforce or unify or otherwise strengthen the absorbent web. The adhesive coating in the absence of a fibrous or absorbent web may itself be sufficiently porous to permit transfer of image-forming components.

The thin inner film 12 of FIGURES l and 2 retracts or shrinks to a lace-like porous or perforate structure when heated to temperatures available in the thermocopying process described, and which may be in the neighborhood of 250 C. Thermoplastic oriented or tensilized polymeric films of minimum thickness are preferred. The same film may be used as the permanently impermeable continuous outer film 14, since the heat produced at the irradiated image of the original is ordinarily dissipated sufi'lciently within the intermediate sheet material to avoid softening, retraction and perforation oft he outer film. Thicker films are more easily handled, however, and are preferred for the outer layer.

It will be appreciated that all of the components of the sheet material must be so selected and associated as to produce a structure which is transmissive of the radiant energy employed when providing a heat-pattern in accordance with the process indicated in FIGURE 1. Radiations rich in infra-red are ordinarly employed in these thermographic front-printing processes, and com ponents have previously been described which are sutficiently non-absorptive of infra-red radiation to be successfully used in these novel sheet structures. On the other hand, heat-patterns otherwise obtained are also effective in forming the porous image areas 16. For example, brief contact with heated metal type faces, particularlythrough a thin intervening silk screen or superficial surface coating of protective lubricant, produces a corresponding porous image pattern in the thin film 12; and other ways of applying an effective heat-pattern are known. For such procedures, the sheet material need not be radiation-tramsmissive.

The sheet material 40 of FIGURE 3 includes neither an outer film layer nor an image-forming component, but instead consists only of a thin tensilized plastic film 41 and a fibrous web 42. Surprisingly, this form of sheet material, when first subjected to a heat-image and thereby provided with corresponding porous image areas, 46, is found to be capable of causing image formation, as indicated at areas 47, in a partially radiation-absorbent visibly heat-sensitive copy-sheet 48 under brief intense irradiation as in thermographic back-printing procedures.

The following specific examples will further illustrate the practice of the invention.

Example 1 Tensilized quarter-mil (.00025 inch) Mylar polyethylene terephthalate polyester film is laminated to a thin porous tissue paper (7 /2 pound Super Flexrope paper) which is first impregnated with a 15% solution in ethylene dichloride of a polymeric polyester of stoichiometric equivalents of polyethylene glycol and a mixture of equal weights of isophthalic and terephthalic acids. After drying, the still porous paper is next impregnated with a molten mixture of one part of Oil Black BT aniline dye in seven parts of Piccolastic thermoplastic resin melting at about 75 C., and the mixture is allowed to cool and solidify. A two mil (.002 inch) film of VBA 9925 vinyl chloride-vinyl acetate copolymer is then heatpressed upon the resin-coated sheet to form a unitary three-layer composite which may be handled, rubbed against white paper, and otherwise manipulated as in the preparation of copies Without transfer of color or delamination of the sheet.

The sheet is placed with the Mylar surface in contact with a portion of a printed page, such as a newspaper, which -is then briefly exposed to intense radiation through the sheet as in thermographic front-printing.

The sheet is next placed with the Mylar surface in contact with a sheet of white paper and is heated from the reverse surface by contact with a clean metal platen at 120 C. A copy of the printed original is obtained in the form of black images on the white paper background. Additional copies are obtained by heating the intermediate sheet in contact with additional sheet of white paper. The metal platen remains clean-surfaced.

Example 2 A mixture of one part cetyl alcohol, two parts hexanediol, and one-half part of Crystal Violet 6B replaces the mixture of dye and resin employed in Example 1. The sheet material produces brilliant blue image areas on the white paper by the copying procedures of Example 1 with the platen temperature at about 65 C. Effective copies on white fabric as well as paper receptor sheets may also be produced by subjecting the composite to brief intense irradiation as in thermographic back-printing.

Example 3 A mixture of seven parts Piccolastic resin and one part of behenoyl pyrogallate replaces the mixture of dye and resin employed in Example 1. The sheet material is substantially colorless. After front-printing against a printed original, the sheet is placed against a receptor sheet having a thin surface coating of silver behenate and resinous binder on white paper, and heat and pressure are applied with a smooth metal platen heated to about 275 F. A copy is obtained having black infrared-absorbent image areas on a white reflective background.

With the platen at somewhat lower temperatures, no image is immediately observed on the treated receptor sheet; but subsequent heating of the receptor sheet to about 275 F. causes the development of the black image areas.

Example 4 Paper in contact with thin film as in Example 1 is first impregnated with a solution of parts of polyester resin and 26 parts of methyl gallate in 90 parts of tetrahydrofurane. Piccolastic resin is then added in molten form, followed by a 2-mil vinyl resin film as in Example 1. The sheet material is substantially colorless. Under the procedures and with the receptor sheets described in Example 3 and with the platen at 135 C. there are proquantity of Lemac 1000 polyvinyl acetate resin.

Example 5 To a concentrated dye solution prepared by acetone extraction of Plasto Violet MB organic dye is added a The solution is used to impregnate and unify the paper and to bond there to the polyester and vinyl resin films as used in Example 1. The dark violet sheet material thus produced provides blue image areas on white paper when employed as described in Example 1 and with the platen at C., at which temperature the dye used is readily volatile. With substitution of Nacelin Black NR" for the Plasto Violet MB and with a platen temperature of 150 C., brownish-black images are produced on white paper receptor sheets. Copie having improved appearances and permanence are prepared by substituting for the paper receptor sheet a treated paper having a surface coating of a mixture of 15 parts of polyester resin and 20 parts of precipitated calcium carbonate in parts of ethylene dichloride, and by subjecting the composite to brief intense radiation under thermographic back-printing procedures rather than heating with the heated platen.

Example 6 A partially processed sheet material prepared by combining the Mylar film and tissue paper as described in Example 1, and after drying but before application of the molten mixture of resin and dye, is combined with the vinyl copolymer film under heat and pressure. The resulting three-layer sheet material is placed with the polyester film surface against a printed original and the composite is briefly intensely irradiated by thermographic front-printing procedures. The processed sheet is then placed with the perforate polyester film against a visibly heat-sensitive copy-sheet having a partially radiation-absorptive surface layer containing silver behenate and protocatechuic acid or other equivalent phenolic reducing agent in physically distinct and chemically interre'active relationship in ethyl cellulose or other filmforming binder, and the new composite is similarly irradiated. A copy is produced having brownish-black image areas correseponding to the printed original. A similar effect is obtained using the partially processed combination of Mylar film bonded to porous paper in the absence of the vinyl copolymer surface film.

The foregoing illustrative examples employ materials and components which have been found to provide useful results but the practice of the invention is not restricted thereto, as will appear from the following further illustrations.

One-half mil tensilized polypropylene film has proved a useful replacement for the one-quarter mil Mylar polyester film; since it is a somewhat softer film and shows a tendency toward tackiness when heated, it is found desirable to apply a minimal sizing coat, for example of dimethyl silicone fluid, over the exposed surface of the film before subjecting the sheet to a heatimage. Silicone fluid is also advantageously applied to the Mylar polyester film of Example 1 when the same is used in making copies of graphic intelligence printed with inks containing thermoplastic resin components. Polystyrene film of 1 /2 mil thickness has also been used.

Similarly, one mil polyvinyl fluoride film has been substituted for the two mil vinyl copolymer outer film layer. The thinner film produces a less bulky final product and increases the heat-resistance of the outer surface, an important consideration when using a heated platen or the like for transfer of image-forming components. Resistance to solvents is also markedly improved. The polyvinyl fluoride film is conveniently bonded to the surface of the impregnated paper by an intervening primer coating of thermoplastic vinyl acetate polymer applied from solution to the film and hot pressed against the paper layer.

Transparent films of regenerated cellulose (Cellophane) are useful as the outer film layer, particularly where thermographic means are employed in preparing the intermediate copy; thin opaque aluminum or other metal foil may be used where the heat-image is supplied from heated type faces. These and other analogous permanently impermeable pre-formed membranes or films are, like the polyvinyl fluoride film, particularly resistant to heat and solvents.

Various volatile reactant materials may replace the methyl gallate of Example 4 or the behenoyl pyrogallate of Example 3, depending on the nature of the co-reactant contained in the receptor sheet. 1-hydroxy-4-methoxynaphthalene is particularly effective in conjunction with noble metal salts such as silver behenate, and is also useful with iron salts, for example ferric steal-ate. Large numbers of volatile dyes may be used in place of those specified in Example 5, with transfer temperatures extending from as low as about 100 C. to well above 200 C. Dyes such as Auramine Base, Autol Brilliant Red BND, Acetamine Scarlet B, Oil Blue A, Sudan Dark Brown BG Ex., and Alizarine are representative.

What is claimed is as follows:

1. Method of making copies of a graphic original comprising: applying a heat-pattern corresponding to the image-forming pattern of said original to the thermoplastic film surface of a heat-sensitive sheet material comprising in order a thin tensilized continuous thermoplastic film, a thin stratum of porous fibrous material containing a transferable image-forming material, and a heat-resistant continuous film, to render said thermoplastic film porous at the heat-pattern areas; placing said sheet material with the perforate film in pressure-contact with a receptor sheet; and applying heat to the exposed surface of said sheet material to cause transfer of said image-forming material through said perforate film and to said receptor sheet.

2. The method of claim 1 in which transfer of imageforming material is accomplished by contacting the exposed surface of the sheet material with a heat source having a surface temperature within the range of about IUD-200 C.

References Cited by the Examiner UNITED STATES PATENTS 1,354,478 10/1920 Gestetner 101129 1,489,706 4/1924 Loebcke 101129 2,740,896 4/1956 Miller 250 2,919,349 12/1959 Kuhrmeyer et al 250-65 ROBERT E. PULFREY, Primary Examiner.

DAVID KLEIN, Examiner. 

1. A METHOD OF MAKING COPIES OF A GRAPHIC ORIGINAL COMPRISING: APPLYING A HEAT-PATTERN CORRESPONDING TO THE IMAGE-FORMING PATTERN OF SAID ORIGINAL TO THE THERMOPLASTIC FILM SURFACE OF A HEAT-SENSITIVE SHEET MATERIAL COMPRISING IN ORDER A THIN TENSILIZED CONTINUOUS THERMOPLASTIC FILM, A THIN STRATUM OF POROUS FIBROUS MATERIAL CONTAINING A TRANSFERABLE IMAGE-FORMING MATERIAL, AND A HEAT-RESISTANT CONTINUOUS FILM, TO RENDER SAID THERMOPLASTIC FILM POROUS AT THE HEAT-PATTERN AREAS; PLACING SAID SHEET MATERIAL WITH THE PERFORATE FILM IN PRESSURE-CONTACT 